<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title></title>
    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
    <script src="https://cdn.bootcdn.net/ajax/libs/vue-router/3.4.8/vue-router.min.js"></script>
</head>

<body>
    <div id='app'>
        <input type="text" v-model:value=num1>+
        <input type="text" v-model:value=num2>=
        <button @click="add()"> =</button>
        <input type="text" v-model:value=num3>
    </div>
    <script>
        const vm = new Vue({
            el: '#app',
            data: {
                num1: "",
                num2: "",
                num3: "",
            },
            methods: {
                add() {
                    this.num3 = Number(this.num1) + Number(this.num2)
                }
            },
            updated() {
                this.num3 = Number(this.num1) + Number(this.num2)
            }

        })
    </script>
</body>

</html>